KR101085834B1 - Light-diffusion plate - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing plate used for a backlight unit, an illumination device, and the like of a liquid crystal display, and provides a light diffusing plate including a polystyrene resin having a polycarbonate resin and methacrylic acid as a base resin of a base layer.

Description

Light-diffusion plate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusion plate used for a backlight unit, an illumination device, or the like of a liquid crystal display.

Conventional light diffusion plate made of methyl methacrylate resin has excellent optical properties such as total light transmittance but low dimensional stability, so it is used with cold cathode fluorescent lamps and light sources such as LEDs to change the light when temperature changes by lighting and turning off. Moisture absorption rate of the diffusion plate can be easily changed, there is a problem such as bending, deformation such as wrinkles, cracking accompanying. That is, there is a problem that deformation such as bending phenomenon occurs in a high temperature and high humidity environment (Japanese Patent Application Laid-Open No. 07-100985, Japanese Patent Application Laid-open No. 08-198976).

In order to solve this problem, a light diffusion plate using polycarbonate resin having excellent dimensional stability due to relatively high light transmittance, high heat resistance and high water absorption is proposed, but in the case of a light diffusion plate to which polycarbonate resin is applied, Although high dimensional stability is exhibited by heat resistance and water absorption, there is a problem in that yellowing occurs when exposed to a light source for a long time due to low light resistance, and has a disadvantage of being expensive.

Accordingly, the present inventors confirmed that the present invention can provide a light diffusion plate capable of suppressing warpage by applying a polystyrene resin having a similar refractive index to a polycarbonate resin and having a relatively low price and excellent thermal characteristics. The invention was completed.

Therefore, an object of the present invention is to provide a light diffusion plate having excellent heat resistance and no bending phenomenon.

As one embodiment of the present invention for achieving the above object, a base resin of the base layer comprises a polycarbonate resin and a polystyrene resin, the polystyrene resin comprises a light diffusion plate comprising a polystyrene resin having methacrylic acid to provide.

According to an embodiment of the present invention, the polystyrene resin having methacrylic acid may be used in an amount of 10 to 90% by weight based on the total weight of the polystyrene resin in the base resin of the base layer.

According to the exemplary embodiment of the present invention, the base resin may have a mixed weight ratio of polycarbonate resin and polystyrene resin of 9: 1 to 1: 9.

According to an embodiment of the present invention, one or both surfaces of the base layer may further include a surface layer including the same or different base resin of the base resin of the base layer.

According to the exemplary embodiment of the present invention, the tan δ peak temperature of the dynamic viscoelasticity of the polystyrene resin may be 120 ° C. or more and less than 150 ° C.

The present invention can provide a light diffusing plate which is excellent in thermal properties and does not cause warpage.

Hereinafter, the present invention will be described in more detail.

The present invention relates to a light diffusion plate using a polycarbonate resin and a polystyrene resin as a base resin of the base layer, wherein the polystyrene resin includes a polystyrene resin having methacrylic acid represented by the following formula (1).

<Formula 1>

CH ₂ = C (CH ₃ ) COOH

The polystyrene resin having the methacrylic acid of Formula 1 has a higher dynamic viscoelastic tan δ peak temperature than the conventional polystyrene resin, specifically, the dynamic viscoelastic tan δ peak temperature ranges from 120 ° C. to less than 150 ° C. When using a resin in the range, it is advantageous because the rate of dimensional change due to the thermal change is reduced.

According to an embodiment of the present invention, a polycarbonate resin and a polystyrene resin are mixed and used as the base resin of the base layer. In order to increase the heat resistance of the base resin, it is preferable to include the polystyrene resin having the methacrylic acid in the polystyrene resin. desirable. Such polystyrene resin preferably has a molecular weight of 200,000 to 250,000.

In consideration of the heat resistance of the light diffusion plate, it is preferable to use 10 to 90% by weight of the polystyrene resin having the methacrylic acid with respect to the total weight of the polystyrene resin used for the base resin of the light diffusion plate of the present invention.

On the other hand, the base resin used in the light diffusion plate of the present invention may be used by mixing a polycarbonate resin and a polystyrene resin in a weight ratio of 1: 9 to 9: 1. In order to take advantage of the flexibility and dimensional stability of the polycarbonate, and to take advantage of the high absorption and strength of polystyrene, it is preferable to mix each content to be at least 10% by weight or more.

The polycarbonate resin is a commonly used aromatic polycarbonate resin, and is a linear or branched carbonate homopolymer, polyester copolymer prepared by reacting dihydroxy phenol with phosgene or by reaction of dihydroxy phenol with a carbonate precursor. Coalescing or mixtures of one or more thereof. The dihydroxy phenol is 2,2-bis (4-hydroxyphenyl) propane (ie bisphenol A), bis (4-hydroxy phenyl) methane, 2,2-bis (4-hydroxy-3,5 -Dimethylphenyl) propane and 1,1-bis (4-hydroxyphenyl) cyclohexane and the like; the carbonate precursor includes diphenyl carbonate, carbonyl halide and diaryl carbonate, and is 300 ° C under ASTM D1238 standard conditions. The melt index (MI) at 1.2 kg load is preferably in the range of 7 to 30 g / 10 min.

For the mixing of the polycarbonate resin and the polystyrene resin, a twin screw extruder having a screw diameter of 30 mm was used, and a molding temperature was prepared by melt kneading at 200 rpm to 300 ° C., preferably 250 ° C., at 250 rpm.

In the case of the multilayer light diffusion plate, the surface layer is further included on one or both surfaces of the substrate layer in addition to the above-described substrate layer. Although the base resin of the surface layer is not particularly limited, acrylic resins or styrene-acrylic copolymer resins may be used. have.

The acrylic resin may be a methacrylic acid alkyl ester such as methyl methacrylate, ethyl methacrylate, butyl methacrylate or 2-ethylhexyl methacrylate; Alkyl acrylates such as methyl acrylate, ethyl acrylate and butyl acrylate; Methacrylic acid cycloalkyl esters such as cyclohexyl methacrylate, 2-methylcyclohexyl methacrylate and dicyclopentanyl methacrylate; Acrylic acid cycloalkyl esters such as cyclohexyl acrylate and 2-methylcyclohexyl acrylate; Methacrylic acid aryl esters such as phenyl methacrylate and benzyl methacrylate; It is preferable that it is any one homopolymer or their copolymers chosen from acrylic acid aryl esters, such as phenyl acrylate and benzyl acrylate.

As the styrene-acrylic copolymer resin, the above-mentioned resin is used as the acrylic monomer, and the styrene monomer may be styrene or substituted styrene. Substituted styrenes include alkyl styrenes such as α-methylstyrene, halogenated styrenes such as chlorostyrene, vinyl styrene, and the like, and if necessary, two or more styrene monomers may be used in combination.

At this time, it is preferable that the weight ratio of the acryl-type monomer and styrene monomer copolymerized is 6: 4-1: 9 in consideration of the binding force with a base material layer.

The substrate layer or the surface layer may further include a light diffusing agent, which is usually the same refractive index with the base resin, is used to increase the light diffusion rate, various organic and inorganic particles are used. In this case, the light diffusing agent exhibits a light diffusing effect even with a small amount when the refractive index with the base resin is large, but a relatively large amount should be included when the refractive index difference is small.

Examples of organic particles typically used include methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid and hydroxyethyl methacrylate. , Hydroxypropyl methacrylate, hydroxy ethyl acrylate, acrylamide, metyrol acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate polymer Or acrylic polymer particles such as copolymers or terpolymers thereof; Olefin polymer particles such as polyethylene and polypropylene; Multi-layered multicomponent particles, siloxane-based polymer particles, tetrafluoroethylene-based particles formed by forming copolymer particles of acryl and olefin, particles of the homopolymer, copolymer or terpolymer, and then covering the layers with other monomers. Particles and the like.

On the other hand, examples of the inorganic light diffusing particles include calcium carbonate, barium sulfate, silicon oxide, aluminum hydroxide, titanium oxide, zirconium oxide, magnesium fluoride, talc, glass, mica and the like. Normally, the organic particles have excellent light diffusivity compared to the inorganic particles, and may be used in combination of two or more types of light diffuse particles if necessary.

When the surface layer further includes a light diffusing agent, the light diffusion effect is further increased, and the light diffusing particles protrude to the surface of the surface layer to have an embossed shape, thereby achieving an effect of having a matte surface and a low reflectance. . At this time, the surface roughness of the surface layer is suitably about 0.1 ~ 50㎛, if the roughness is more than 50㎛ surface impact strength is insufficient, if the roughness is less than 0.1㎛ the matt effect.

The content of the light diffusing agent used in the base layer or the surface layer of the present invention is 0.01 to 35% by weight, preferably 0.5 to 15% by weight, of the total composition of the base resin or the surface layer of the base layer. If the amount of the light diffusing agent is less than 0.01% by weight, it is difficult to expect sufficient light diffusion effect and concealability, and if it is more than 35% by weight, light transmittance is not good. At this time, the content of the light diffusing agent may be determined according to the difference in refractive index with the base resin.

On the other hand, in the present invention, a light stabilizer may be added to the base layer or the surface layer, the light stabilizer that can be added as a UV absorber and a radical scavenger having a maximum absorption wavelength in the range 250nm ~ 380nm can maximize the light stabilizer effect Ultraviolet stabilizers of hindered amines are preferred. They must be effective for a long time, must not be evaporated or extracted to be freed or removed from the sheet, and an absorbent with good compatibility with the substrate should be selected.

Examples of the ultraviolet absorber include cyanoacrylic, salicylate, malonic ester, oxalanilide, diketone, hydroxy benzophenone, hydroxy benzotriazole, organometallic, and the like. The above can be used in combination.

Examples of ultraviolet stabilizers include piperidinyl esters, oxazolidines and piperidinooxazolidines, piperidisspiroacetals, and diazacycloalkanones, and two or more selected from them can be used in combination. .

The content of the light stabilizer is 0.01% by weight to 5% by weight in each of the total resin compositions of the base layer or the surface layer, preferably 0.1% by weight to 2% by weight. In particular, by including them in the surface layer, it is possible to obtain the expected light stability effect without lowering the total light transmittance and physical properties of the substrate layer, and also bring about the effect of cost reduction.

When the light diffusion plate of the present invention forms a surface layer on one surface or both surfaces of the substrate layer, it can be produced by a method such as coextrusion molding, lamination, thermal bonding, surface coating, etc., which are well-known techniques.

The light diffusion plate of the present invention can be used for various applications indoors and outdoors. That is, it can be used for signage, lighting signage, lighting cover, glass showcase, and preferably used as a light diffusion plate for display. Representative examples of display light diffusers include light diffusers for liquid crystal display backlights or edge light type backlights.

Hereinafter, examples of the present invention will be described in more detail, but the scope of the present invention is not limited to these examples.

Compositions and composition ratios of Examples and Comparative Examples are as shown in the following [Table 1] to [Table 4].

The base resin of the base material layer was uniformly charged with polycarbonate and polystyrene in the composition ratio shown in the table, and melt kneaded at a temperature of 250 ° C. with a twin screw extruder.

At this time, the polycarbonate was used that the melt index (MI) at 300 ℃, 1.2kg load under the conditions of ASTM D1238 standard 22g / 10min.

Molding was coextruded at a screw diameter of 135 mm and 60 mm, respectively, and the molding temperature was performed at 250 ° C.

Table 1 is a case of a light diffusion plate formed only of the base layer, Table 2 is a case of the light diffusion plate formed with a surface layer on both sides, Table 3 is a light diffusion plate formed of only the base layer as a comparative example and not using a heat-resistant polystyrene resin In the case of a plate, Table 4 shows a case of a light diffusion plate in which surface layers are formed on both surfaces and heat-resistant polystyrene resin is not used.

In Examples and Comparative Examples of Table 1 and Table 3 formed only of the substrate layer, the thickness of the substrate layer was 2.0 mm, and in Examples and Comparative Examples of Table 2 and Table 4 having surface layers formed on both surfaces of the substrate layer, the substrate layer was used. The thickness of each was 1.8 mm and the thickness of the surface layer was 0.1 mm on both sides.

The materials used in Examples and Comparative Examples are as follows.

* PC: Polycarbonate (polycarbonate obtained by reacting 2,2-bis (4-hydroxyphenyl) propane with phosgene, LG Dow (trade name Caliber 300-22)

* PS-1: Polystyrene having a molecular weight of 200,000 to 250,000 with methacrylic acid (the tanδ peak temperature of the dynamic viscoelasticity is 120 ℃ or more and less than 150 ℃, Toyo Styrene (trade name, T-080)

* PS-2: Polystyrene having molecular weight of 200,000 to 250,000 (Danδ peak temperature of dynamic viscoelasticity is 80 ℃ or more and less than 120 ℃)

* MS: Styrene-acrylate copolymer resin (styrene content 80 wt%, acrylate content 20 wt%)

Specific evaluation method of the tan δ peak temperature of the dynamic viscoelasticity is as follows. Dynamic viscoelasticity was measured by the following setting, and the point which shows the highest value among the inflection points of tan-delta obtained was made into the tan-delta peak. In other words, the tanδ peak temperature is the temperature at the highest point of the tanδ value.

* Measuring device: Seiko Electronics DMS 200

* Sample shape: 9mm × 40mm

* Measurement mode: tension mode

* Profile: 20 ℃ ~ 400 ℃, temperature increase rate 3 ℃ / min

* Frequency: 1Hz, 5Hz, 10Hz

* Lamp. (AC Distortion Amplitude Target): 20㎛

* Fbase (minimum tension during measurement): 0g

* F0gain (coefficient when changing tension according to AC force amplitude during measurement): 3.0

As the composition of the light diffusing plate according to the Examples and Comparative Examples, the base material layer was 0.2 parts by weight of silicone resin beads (average particle size 2 μm) as a light diffusing agent, and a UV absorber as a light stabilizer to the base resin and the compatibilizer according to the composition of Table 1. 0.05 weight part of phosphorus B-Cap (tetraethyl-2,2 '-(1,4-phenylene- dimethylidene) -bismalonate) is mixed, and the surface layer at the time of forming a surface layer is according to the composition of Table 1. B-Cap (tetraethyl-2,2 '-(1,4-phenylene-dimethylidene) -bis, which is an ultraviolet absorber, is used as a light diffusing agent to 2 parts by weight of silicone resin particles (average particle diameter: 2 µm) and a light stabilizer. Malonate) was mixed at 0.5 part by weight.

The heat diffusion, bending resistance, light transmittance, impact strength, haze, water absorption rate, and heat deflection temperature of the light diffusing plates manufactured in the above Examples and Comparative Examples were measured by the following methods, and are shown in Tables 5 to 8. It was.

(1) heat deflection temperature

It measured by the ASTM D648 method.

(2) bending resistance

A light diffuser plate was mounted on a 32 ″ size backlight unit and allowed to stand for 96 hours at 70 ° C and 90% relative humidity.

(3) light transmittance

Measured by ASTM D1003 method

(4) impact strength

Measured by ASTM D1256 method

(5) haze

Measured by ASTM D1003 method.

(6) water absorption rate

The light diffusion plate was cut into 10 × 10 cm, and then left at 25 ° C. for 24 hours in water to measure moisture absorption from the change in weight.

division Heat deflection temperature
(℃) Flexural resistance
(mm) Impact strength
(J / m) Light transmittance
(%) Hayes
(%) Water absorption
(%) Example 1 123.1 0.22 25.6 73.1 99.2 0.20 Example 2 126.4 0.25 28.7 72.6 99.3 0.21 Example 3 130.9 0.36 32.1 73.5 98.9 0.25 Example 4 120.8 0.18 24.3 74.2 99.1 0.15 Example 5 122.4 0.23 27.2 72.8 99.2 0.24 Example 6 118.6 0.12 23.4 73.4 98.8 0.12 Example 7 124.5 0.16 28.1 73.2 99.3 0.18 Example 8 124.2 0.20 26.3 74.4 98.7 0.21 Example 9 125.8 0.23 27.5 73.1 99.1 0.24 Example 10 129.6 0.31 33.2 72.9 98.7 0.26 Example 11 121.1 0.15 25.8 72.4 98.6 0.18 Example 12 123.2 0.18 26.7 73.5 98.9 0.21 Example 13 119.5 0.10 25.1 73.9 99.4 0.11 Example 14 123.8 0.13 29.5 74.1 99.2 0.14

division Heat deflection temperature
(℃) Flexural resistance
(mm) Impact strength
(J / m) Light transmittance
(%) Hayes
(%) Water absorption
(%) Comparative Example 1 101.9 0.45 24.9 72.8 98.6 0.20 Comparative Example 2 105.4 0.57 27.3 73.4 99.1 0.21 Comparative Example 3 114.3 0.61 31.6 72.8 98.2 0.25 Comparative Example 4 100.4 0.32 23.8 72.5 98.4 0.15 Comparative Example 5 104.2 0.45 26.7 73.4 99.3 0.24 Comparative Example 6 97.3 0.22 24.3 71.9 98.48 0.12 Comparative Example 7 101.3 0.32 29.0 73.3 98.2 0.18 Comparative Example 8 109.4 0.28 27.6 72.1 99.1 0.21 Comparative Example 9 100.8 0.33 26.7 74.8 98.1 0.24 Comparative Example 10 117.1 0.58 32.5 72.4 98.9 0.26 Comparative Example 11 98.8 0.34 24.7 73.6 99.3 0.18 Comparative Example 12 104.7 0.36 27.2 71.5 98.3 0.21 Comparative Example 13 101.2 0.21 24.6 74.2 99.2 0.11 Comparative Example 14 101.5 0.28 29.1 72.8 98.2 0.14

As a result of the physical property evaluation, as can be seen from the comparison between the Example and the comparative example, when using a polystyrene resin having methacrylic acid compared to the case of using a conventional polystyrene resin, the optical properties such as light transmittance and haze, without significant change in deformation by heat It can be seen from the bending resistance and the heat deformation temperature that it has more stable high heat resistance.

In addition, as the content of the polystyrene resin increases, the change in light transmittance or haze does not change significantly within a certain level range, but it can be seen that the water absorption rate is lowered and the bending resistance is also lowered.

Claims (5)

As a base resin of the substrate layer, a polycarbonate resin and a polystyrene resin are included. The polystyrene resin is a light diffusion plate including a polystyrene resin having methacrylic acid. 10 to 90% by weight of the polystyrene resin having the methacrylic acid based on the total weight of the polystyrene resin in the base resin of the base layer, The light diffusion plate, characterized in that the tan δ peak temperature of the dynamic viscoelasticity of the polystyrene resin is 120 ° C or more and less than 150 ° C. delete The method of claim 1, The base resin is a light diffusion plate, characterized in that the mixing weight ratio of polycarbonate resin and polystyrene resin is 9: 1 to 1: 9. The method of claim 1, And a surface layer on one or both surfaces of the substrate layer, the surface layer including a base resin that is the same as or different from the base resin of the substrate layer. delete